The present invention is directed to a dual circuit multiple effect absorption refrigeration system in which a single-effect high temperature refrigeration loop is combined with a lower temperature double-effect refrigeration loop by a double-condenser coupling with both of the generators in the double-effect refrigeration loop. This arrangement provides for internal heat recovery at a level essentially corresponding to that achieved by a triple-effect refrigeration loop using a double-condenser coupling and is improved thereover by enabling an alcohol or other heat and mass transfer additive to be used in the lower temperature double-effect refrigeration loop for improving absorber performance and the thermal efficiency of the overall system.
This invention was made with the support of the United States Government under contract No. DE-AC05-84OR21400 awarded by the U.S. Department of Energy, Office of Building Technologies. The United States Government has certain rights in this invention.
Recent developments in absorption refrigeration systems have provided significant improvements in the thermal efficiency or coefficient of performance (COP) over the basic commercial single-effect absorption refrigeration system which utilizes a single-effect absorption system comprising a generator, a condenser, an evaporator, and an absorber operatively coupled together and which typically provides a COP in the range of about 0.6 to 0.7.
An increase in the COP to about 1.0 to 1.3 was provided by the development of a double-effect refrigeration absorption system in which two generators with condensers operating at different temperatures are coupled to a single evaporator and absorber. The heat of condensation in the condenser coupled to the high temperature generator is used as the heat source for the lower temperature generator.
A corresponding increase in COP was achieved by the development of the dual-loop refrigeration absorption systems which utilized two separate single-effect refrigeration absorption loops operating at different temperatures. In this arrangement the higher temperature refrigeration loop provided the operating heat for the lower temperature refrigeration loop through a heat exchange coupling between at least the condenser in the higher temperature loop and the generator in the lower temperature loop. A typical dual-loop absorption refrigeration system is described in U.S. Pat. No. 4,542,628.
A different arrangement of the single-effect refrigeration loops utilized in the above-described dual-loop refrigeration system resulted in a triple-effect refrigeration system wherein the externally applied heat is utilized internally three times to produce the desired cooling effect at the evaporators. Such a triple-effect absorption refrigeration system is described in U.S. Pat. No. 4,732,008 and provides an increase in COP over that achieved with the dual-loop refrigeration systems.
Triple effect absorption refrigeration systems also includes arrangements wherein three generators and condensers with the condensers being individually coupled to a single evaporator. A typical triple-effect system utilizing such a three generator arrangement is described in U.S. Pat. Nos. 4,520,634 and 4,531,374 (FIG. 44G). The three sets of generators and condensers function at different temperatures and pressures. External heat is applied to the high temperature third generator while heat rejection from the high temperature third condenser is used to heat the medium temperature second generator. The heat of condensation from the medium temperature second condenser is used to heat the low temperature first generator. The condensed refrigerant from the first, second, and third condensers is evaporated in the evaporator to provide the desired refrigeration effect. The COP for such a triple-effect system is about 1.3 which corresponds to the higher thermal efficiencies provided by the double-effect and dual-loop systems described above.
More recent developments in multiple or triple-effect refrigeration systems which provided an increase in COP over earlier triple-effect refrigeration systems such as described above utilize an arrangement wherein the high temperature third condenser is double coupled to provide heat to both the medium temperature second generator and to the low temperature first generator for increasing internal heat recovery. Triple-effect refrigeration systems which utilize such a double-condenser coupling are described in U.S. Pat. Nos. 4,551,991 and 5,205,136. These patents directed to the triple-effect refrigeration system utilizing the double-condenser coupling as well as the other aforementioned patents are incorporated herein by reference.
While the triple-effect absorption refrigeration systems using a double-condenser coupling provide for significant improvements in thermal efficiency over other known multiple-effect absorption refrigeration system there is still a problem or shortcoming inherent in triple-effect absorption refrigeration systems operating in a relatively high temperature range which prevents these high temperature triple-effect systems from realizing their full potential with respect to thermal efficiency. For example, in triple-effect absorption system described in U.S. Pat. No. 5,205,136 the operating temperature of the high temperature third generator is required to be in a range of about 360.degree. to 500.degree. F. in order to achieve the improvements in thermal efficiency gained by utilizing the double-condenser coupling. In this and other prior triple-effect refrigeration systems the third generator and other components subjected to high temperatures greater than about 400.degree. F. may be constructed of corrosion resistant materials in order to permit operation at temperatures higher than about 400.degree. F. However, a standard heat and mass transfer additive such as 2-ethyl-1-hexanol as beneficially used in lower temperature single, double and dual effect absorption refrigeration systems for increasing absorber performance can not be similarly utilized in such high temperature triple-effect refrigeration systems since such know heat and mass transfer additives undergo decomposition at temperatures greater than about 360.degree. F. Thus, the operation of high temperature triple-effect refrigeration systems achieved without the use of a standard alcohol or other known heat and mass transfer additive suffers reduced absorber performance and consequently a reduction in potential thermal efficiency.